IRQ: Maintain regs pointer globally rather than passing to IRQ handlers

Maintain a per-CPU global "struct pt_regs *" variable which can be used instead
of passing regs around manually through all ~1800 interrupt handlers in the
Linux kernel.

The regs pointer is used in few places, but it potentially costs both stack
space and code to pass it around.  On the FRV arch, removing the regs parameter
from all the genirq function results in a 20% speed up of the IRQ exit path
(ie: from leaving timer_interrupt() to leaving do_IRQ()).

Where appropriate, an arch may override the generic storage facility and do
something different with the variable.  On FRV, for instance, the address is
maintained in GR28 at all times inside the kernel as part of general exception
handling.

Having looked over the code, it appears that the parameter may be handed down
through up to twenty or so layers of functions.  Consider a USB character
device attached to a USB hub, attached to a USB controller that posts its
interrupts through a cascaded auxiliary interrupt controller.  A character
device driver may want to pass regs to the sysrq handler through the input
layer which adds another few layers of parameter passing.

I've build this code with allyesconfig for x86_64 and i386.  I've runtested the
main part of the code on FRV and i386, though I can't test most of the drivers.
I've also done partial conversion for powerpc and MIPS - these at least compile
with minimal configurations.

This will affect all archs.  Mostly the changes should be relatively easy.
Take do_IRQ(), store the regs pointer at the beginning, saving the old one:

	struct pt_regs *old_regs = set_irq_regs(regs);

And put the old one back at the end:

	set_irq_regs(old_regs);

Don't pass regs through to generic_handle_irq() or __do_IRQ().

In timer_interrupt(), this sort of change will be necessary:

	-	update_process_times(user_mode(regs));
	-	profile_tick(CPU_PROFILING, regs);
	+	update_process_times(user_mode(get_irq_regs()));
	+	profile_tick(CPU_PROFILING);

I'd like to move update_process_times()'s use of get_irq_regs() into itself,
except that i386, alone of the archs, uses something other than user_mode().

Some notes on the interrupt handling in the drivers:

 (*) input_dev() is now gone entirely.  The regs pointer is no longer stored in
     the input_dev struct.

 (*) finish_unlinks() in drivers/usb/host/ohci-q.c needs checking.  It does
     something different depending on whether it's been supplied with a regs
     pointer or not.

 (*) Various IRQ handler function pointers have been moved to type
     irq_handler_t.

Signed-Off-By: David Howells <dhowells@redhat.com>
(cherry picked from 1b16e7ac850969f38b375e511e3fa2f474a33867 commit)

1 files changed, 14 insertions, 14 deletions

diff --git a/drivers/usb/input/hid-core.c b/drivers/usb/input/hid-core.c
index e0fd11605b43..a6738a83ff5b 100644
--- a/drivers/usb/input/hid-core.c
+++ b/drivers/usb/input/hid-core.c
@@ -780,13 +780,13 @@ static __inline__ int search(__s32 *array, __s32 value, unsigned n)
         return -1;
 }
 
-static void hid_process_event(struct hid_device *hid, struct hid_field *field, struct hid_usage *usage, __s32 value, int interrupt, struct pt_regs *regs)
+static void hid_process_event(struct hid_device *hid, struct hid_field *field, struct hid_usage *usage, __s32 value, int interrupt)
 {
         hid_dump_input(usage, value);
         if (hid->claimed & HID_CLAIMED_INPUT)
-                hidinput_hid_event(hid, field, usage, value, regs);
+                hidinput_hid_event(hid, field, usage, value);
         if (hid->claimed & HID_CLAIMED_HIDDEV && interrupt)
-                hiddev_hid_event(hid, field, usage, value, regs);
+                hiddev_hid_event(hid, field, usage, value);
 }
 
 /*
@@ -795,7 +795,7 @@ static void hid_process_event(struct hid_device *hid, struct hid_field *field, s
  * reporting to the layer).
  */
 
-static void hid_input_field(struct hid_device *hid, struct hid_field *field, __u8 *data, int interrupt, struct pt_regs *regs)
+static void hid_input_field(struct hid_device *hid, struct hid_field *field, __u8 *data, int interrupt)
 {
         unsigned n;
         unsigned count = field->report_count;
@@ -822,19 +822,19 @@ static void hid_input_field(struct hid_device *hid, struct hid_field *field, __u
         for (n = 0; n < count; n++) {
 
                 if (HID_MAIN_ITEM_VARIABLE & field->flags) {
-                        hid_process_event(hid, field, &field->usage[n], value[n], interrupt, regs);
+                        hid_process_event(hid, field, &field->usage[n], value[n], interrupt);
                         continue;
                 }
 
                 if (field->value[n] >= min && field->value[n] <= max
                         && field->usage[field->value[n] - min].hid
                         && search(value, field->value[n], count))
-                                hid_process_event(hid, field, &field->usage[field->value[n] - min], 0, interrupt, regs);
+                                hid_process_event(hid, field, &field->usage[field->value[n] - min], 0, interrupt);
 
                 if (value[n] >= min && value[n] <= max
                         && field->usage[value[n] - min].hid
                         && search(field->value, value[n], count))
-                                hid_process_event(hid, field, &field->usage[value[n] - min], 1, interrupt, regs);
+                                hid_process_event(hid, field, &field->usage[value[n] - min], 1, interrupt);
         }
 
         memcpy(field->value, value, count * sizeof(__s32));
@@ -842,7 +842,7 @@ exit:
         kfree(value);
 }
 
-static int hid_input_report(int type, struct urb *urb, int interrupt, struct pt_regs *regs)
+static int hid_input_report(int type, struct urb *urb, int interrupt)
 {
         struct hid_device *hid = urb->context;
         struct hid_report_enum *report_enum = hid->report_enum + type;
@@ -892,7 +892,7 @@ static int hid_input_report(int type, struct urb *urb, int interrupt, struct pt_
                 hiddev_report_event(hid, report);
 
         for (n = 0; n < report->maxfield; n++)
-                hid_input_field(hid, report->field[n], data, interrupt, regs);
+                hid_input_field(hid, report->field[n], data, interrupt);
 
         if (hid->claimed & HID_CLAIMED_INPUT)
                 hidinput_report_event(hid, report);
@@ -1004,7 +1004,7 @@ done:
  * Input interrupt completion handler.
  */
 
-static void hid_irq_in(struct urb *urb, struct pt_regs *regs)
+static void hid_irq_in(struct urb *urb)
 {
         struct hid_device       *hid = urb->context;
         int                     status;
@@ -1012,7 +1012,7 @@ static void hid_irq_in(struct urb *urb, struct pt_regs *regs)
         switch (urb->status) {
                 case 0:                 /* success */
                         hid->retry_delay = 0;
-                        hid_input_report(HID_INPUT_REPORT, urb, 1, regs);
+                        hid_input_report(HID_INPUT_REPORT, urb, 1);
                         break;
                 case -ECONNRESET:       /* unlink */
                 case -ENOENT:
@@ -1193,7 +1193,7 @@ static int hid_submit_ctrl(struct hid_device *hid)
  * Output interrupt completion handler.
  */
 
-static void hid_irq_out(struct urb *urb, struct pt_regs *regs)
+static void hid_irq_out(struct urb *urb)
 {
         struct hid_device *hid = urb->context;
         unsigned long flags;
@@ -1238,7 +1238,7 @@ static void hid_irq_out(struct urb *urb, struct pt_regs *regs)
  * Control pipe completion handler.
  */
 
-static void hid_ctrl(struct urb *urb, struct pt_regs *regs)
+static void hid_ctrl(struct urb *urb)
 {
         struct hid_device *hid = urb->context;
         unsigned long flags;
@@ -1249,7 +1249,7 @@ static void hid_ctrl(struct urb *urb, struct pt_regs *regs)
         switch (urb->status) {
                 case 0:                 /* success */
                         if (hid->ctrl[hid->ctrltail].dir == USB_DIR_IN)
-                                hid_input_report(hid->ctrl[hid->ctrltail].report->type, urb, 0, regs);
+                                hid_input_report(hid->ctrl[hid->ctrltail].report->type, urb, 0);
                         break;
                 case -ESHUTDOWN:        /* unplug */
                         unplug = 1;